feat(macos): open transfer invitations in native share sheet

desktopApp/src/main/kotlin/com/vnidrop/app/MacOsAppKitAppearance.kt

@@ -1,9 +1,12 @@
 package com.vnidrop.app
 
+import com.sun.jna.Callback
 import com.sun.jna.Library
 import com.sun.jna.Native
 import com.sun.jna.NativeLibrary
 import com.sun.jna.Pointer
+import com.sun.jna.Structure
+import java.io.File
 
 internal object MacOsAppKitAppearance {
 	private val objc: ObjCRuntime? by lazy {
@@ -42,10 +45,112 @@ internal object MacOsAppKitAppearance {
 		System.getProperty("os.name").startsWith("Mac", ignoreCase = true)
 }
 
+internal object MacOsShareSheet {
+	private val objc: ObjCRuntime? by lazy {
+		runCatching {
+			NativeLibrary.getInstance("AppKit")
+			Native.load("objc", ObjCRuntime::class.java)
+		}.getOrNull()
+	}
+	private var retainedPicker: Pointer? = null
+	private val systemLibrary: NativeLibrary? by lazy {
+		runCatching { NativeLibrary.getInstance("System") }.getOrNull()
+	}
+	private val dispatch: DispatchRuntime? by lazy {
+		runCatching { Native.load("System", DispatchRuntime::class.java) }.getOrNull()
+	}
+
+	fun share(file: File): Result<Unit> = runCatching {
+		require(file.isFile) { "The invitation file could not be created" }
+		var failure: Throwable? = null
+		val runtime = dispatch ?: error("The macOS main queue is unavailable")
+		// dispatch_get_main_queue() is a C macro on Darwin, so there is no
+		// function for dlsym/JNA to resolve. The macro returns this exported
+		// queue object directly.
+		val queue = systemLibrary?.getGlobalVariableAddress("_dispatch_main_q")
+			?: error("The macOS main queue is unavailable")
+		runtime.dispatch_sync_f(queue, null, DispatchWork { failure = runCatching { show(file) }.exceptionOrNull() })
+		failure?.let { throw it }
+	}
+
+	private fun show(file: File) {
+		val runtime = objc ?: error("AppKit is unavailable")
+		val applicationClass = runtime.objc_getClass("NSApplication") ?: error("NSApplication is unavailable")
+		val application = runtime.objc_msgSend(applicationClass, runtime.sel_registerName("sharedApplication"))
+			?: error("NSApplication could not be opened")
+		val window = runtime.objc_msgSend(application, runtime.sel_registerName("keyWindow"))
+			?: runtime.objc_msgSend(application, runtime.sel_registerName("mainWindow"))
+			?: error("No active macOS window")
+		val contentView = runtime.objc_msgSend(window, runtime.sel_registerName("contentView"))
+			?: error("The active window has no content view")
+		val path = nsString(runtime, file.absolutePath) ?: error("The invitation path is invalid")
+		val urlClass = runtime.objc_getClass("NSURL") ?: error("NSURL is unavailable")
+		val url = runtime.objc_msgSend(urlClass, runtime.sel_registerName("fileURLWithPath:"), path)
+			?: error("The invitation URL could not be created")
+		val arrayClass = runtime.objc_getClass("NSArray") ?: error("NSArray is unavailable")
+		val items = runtime.objc_msgSend(arrayClass, runtime.sel_registerName("arrayWithObject:"), url)
+			?: error("The share item could not be created")
+		val pickerClass = runtime.objc_getClass("NSSharingServicePicker") ?: error("The macOS share sheet is unavailable")
+		val allocated = runtime.objc_msgSend(pickerClass, runtime.sel_registerName("alloc"))
+			?: error("The macOS share sheet could not be allocated")
+		val picker = runtime.objc_msgSend(allocated, runtime.sel_registerName("initWithItems:"), items)
+			?: error("The macOS share sheet could not be created")
+		retainedPicker?.let { runtime.objc_msgSend(it, runtime.sel_registerName("release")) }
+		retainedPicker = picker
+		runtime.objc_msgSend(
+			picker,
+			runtime.sel_registerName("showRelativeToRect:ofView:preferredEdge:"),
+			anchorRect(),
+			contentView,
+			3L,
+		)
+	}
+
+	private fun nsString(runtime: ObjCRuntime, value: String): Pointer? {
+		val stringClass = runtime.objc_getClass("NSString") ?: return null
+		return runtime.objc_msgSend(stringClass, runtime.sel_registerName("stringWithUTF8String:"), value)
+	}
+
+	internal fun validateNativeRectMapping(): Int = anchorRect().size()
+	internal fun hasNativeMainQueue(): Boolean =
+		runCatching { systemLibrary?.getGlobalVariableAddress("_dispatch_main_q") != null }.getOrDefault(false)
+
+	private fun anchorRect() = NSRectByValue().apply {
+		x = 0.0
+		y = 0.0
+		width = 1.0
+		height = 1.0
+		write()
+	}
+}
+
+@Structure.FieldOrder("x", "y", "width", "height")
+internal class NSRectByValue : Structure(), Structure.ByValue {
+	@JvmField var x: Double = 0.0
+	@JvmField var y: Double = 0.0
+	@JvmField var width: Double = 0.0
+	@JvmField var height: Double = 0.0
+}
+
 private interface ObjCRuntime : Library {
 	fun objc_getClass(name: String): Pointer?
 	fun sel_registerName(name: String): Pointer
 	fun objc_msgSend(receiver: Pointer?, selector: Pointer?): Pointer?
 	fun objc_msgSend(receiver: Pointer?, selector: Pointer?, argument: Pointer?): Pointer?
 	fun objc_msgSend(receiver: Pointer?, selector: Pointer?, argument: String): Pointer?
+	fun objc_msgSend(
+		receiver: Pointer?,
+		selector: Pointer?,
+		rect: NSRectByValue,
+		view: Pointer?,
+		edge: Long,
+	): Pointer?
+}
+
+private fun interface DispatchWork : Callback {
+	fun invoke(context: Pointer?)
+}
+
+private interface DispatchRuntime : Library {
+	fun dispatch_sync_f(queue: Pointer?, context: Pointer?, work: DispatchWork)
 }

desktopApp/src/main/kotlin/com/vnidrop/app/main.kt

@@ -3,10 +3,14 @@ package com.vnidrop.app
 import androidx.compose.ui.window.Window
 import androidx.compose.ui.window.application
 import com.vnidrop.app.platform.DesktopAppearanceBridge
+import com.vnidrop.app.feature.send.DesktopShareBridge
 
 fun main() {
 	configureMacOsNativeAppearance()
 	DesktopAppearanceBridge.applyNativeAppearance = MacOsAppKitAppearance::apply
+	if (System.getProperty("os.name").startsWith("Mac", ignoreCase = true)) {
+		DesktopShareBridge.shareFile = MacOsShareSheet::share
+	}
 	application {
 		Window(
 			onCloseRequest = ::exitApplication,

desktopApp/src/test/kotlin/com/vnidrop/app/MacOsShareSheetTest.kt

@@ -0,0 +1,17 @@
+package com.vnidrop.app
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class MacOsShareSheetTest {
+	@Test
+	fun nativeAnchorRectHasTheCocoaLayout() {
+		assertEquals(32, MacOsShareSheet.validateNativeRectMapping())
+	}
+
+	@Test
+	fun nativeMainDispatchQueueCanBeResolved() {
+		assertTrue(MacOsShareSheet.hasNativeMainQueue())
+	}
+}